Web Animations: Pass timeToNextIteration to calculateTimeToNextEffect

This will be used by animations running on the compositor to request a
service on the next iteration boundary.

Review URL: https://codereview.chromium.org/71203002

git-svn-id: svn://svn.chromium.org/blink/trunk@162011 bbb929c8-8fbe-4397-9dbb-9b2b20218538